MC13135 single narrowband FM receiver circuit works and its application circuit
The internal oscillation circuit and the external components MC13135 Pin1 and Pin2 of the vibration level of the composition of a first carrier frequency by the RF input signal from the selected frequency of the LC resonance circuit of MC13135 Pin22 input inside the first mixer stage for mixing , and the difference frequency 10.7MHz first IF signal from the Pin20 output by 10.7 ceramic filters to the selected frequency pin18 internally by the second mixer circuit . Internal oscillator circuit and Pin5 and Pin6 external crystal and capacitors constitute the second stage of the oscillation frequency of a selected lower than the first intermediate frequency ( ie frequency 455kHz) of 10.245MHz. 10.7MHz first IF signal with the second local oscillator frequency mixing, difference frequency which is :10.700-10 .245 = 0.455MHz, i.e. the second intermediate frequency signal is 455kHz .
The second IF signal output from the Pin7 from 455kHz ceramic filters selected frequency , and then into the MC13135 Pin9 limiting amplifier for high- gain amplifier , limiting amplifier stage is the main gain stage of the entire circuit . Pin13 external LC resonant element consisting 455kHz frequency discriminator circuit , the second intermediate frequency signal amplified by the frequency discriminator internally demodulation, and after the voltage level of the audio output of the audio signal amplified by Pin17 .
MC13135 is also equipped with an internal data signal amplification stage , Pin12 the RSSI input terminal , Pin15 to the input of an operational amplifier stage , Pin16 the RSSI output of the buffer amplifier . Pin10 and Pin11 of decoupling capacitors to ensure that the circuit stably.